Plume fluxes in clear and cloudy convective boundary layers

Journal Article · Thu Aug 01 04:00:00 EDT 1991 · Journal of the Atmospheric Sciences; (United States)

DOI:https://doi.org/10.1175/1520-0469(1991)048<1746:PFICAC>2.0.CO;2· OSTI ID:5477198

Schumann, U ^[1]; Moeng, C H ^[2]

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1. DLR, Oberpfaffenhofen (Germany)
2. National Center for Atmospheric Research, Boulder, CO (United States)

From results of large-eddy simulations of the clear convective boundary layer and of a stratus-topped boundary layer, mean properties of [open quotes]plumes[close quotes] that consist of [open quotes]updrafts[close quotes] and [open quotes]downdrafts[close quotes] are determined. The plumes are defined locally by the sign of the vertical velocity or of moisture fluctuation or by a combination of both. As a further alternative, updrafts and downdrafts in which the vertical velocity magnitude exceeds certain threshold values are considered. The first two variants divide the motion field into two streams, whereas in the other variants [open quotes]environmental[close quotes] air forms a separate stream. The computed mean properties are in general agreement with existing measurements. From the results we compute mean vertical fluxes assuming [open quotes]top-hat profiles[close quotes] and compare these with the actual fluxes. It is shown that the most uniform flux approximation is obtained if the plume structure is classified in terms of vertical velocity w. For such [open quotes]w plumes,[close quotes] the top-hat profiles approximate about 60% of the actual fluxes if updrafts and downdrafts are distinguished with zero threshold values just according to the sign of the vertical velocity. A higher percentage is obtained with nonzero threshold values. 23 refs., 40 figs.

• OSTI ID: 5477198
• Journal Information: Journal of the Atmospheric Sciences; (United States), Journal Name: Journal of the Atmospheric Sciences; (United States) Vol. 48:15; ISSN 0022-4928; ISSN JAHSAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
ATMOSPHERIC CIRCULATION
BOUNDARY CONDITIONS
COMPUTERIZED SIMULATION
CONVECTION
ENERGY TRANSFER
FLUID FLOW
HEAT TRANSFER
MASS TRANSFER
METEOROLOGY
PLUMES
SIMULATION
VORTEX FLOW